Liquid-seal expansion roof



' y 21,1929- a. F. H. BOHNHARDT 1,714,209

.LIQUID SEAL EXPANSION ROOF I Filed Feb. 1, 1928 can 7 Patented May -21,1929.

- the tank shell. the trough is shown at 4.

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Application filed February 1, 192 8. Scriai No. 251,195.

, My invention relates to the art 5 Oil Stop age with especial referenceto a tank'roof. An objectiof my invention is to prevent the loss ofvapor through the daily breathing of such tanks caused by variations intemperature between night and; day. As the temperature increases the.vapor in the tank expands and escapes through a relief valve;

'converscly as the tank cools at night, air 10 is drawn into the tankthrough a vacuum relief valve. Such breathing causes large evaporationlosses. By providing a tank "with suflicient"expansibility toaccommodate this volumechange, breathing and evaporation losses arestopped.

Other objects and advantages. will be apparent from the followingdescription of a preferred embodiment of my present invention,-reference being made to the accompanying drawing, in which:

Figure 1 is a section through a tank showing one manner of applyingmyliquid seal expansion roof. 7

Figure 2 is a section through a tank show ing a second manner ofapplying the same. FigureB is a dctailof the liquid seal. Figure 4 is adetail of a. liquid seal relief valve. I

In the application of my invention I provide around the top. of the.tankshell a continuous trough designated by numeral 1. This trough ismade. in sections, each section a single piece of steel bent to theshape shown and welded to the tank shell 2 as at 3. It is desirable tohave the outer peripheral wall 5 of this trough about as high as the topof Suitable bracing to support The tank foot 6 extendsbeyond the tankshell to reach about the center of the trough. A downward extendingskirt 7 is non-leakably secured to the edge of the roof and dips intothe trough. The trough is filled with water and, as skirt 7 extendsbelow the water level a gas tight joint is made between the tank shelland the roof. The roof floats on the vapor in the tank. The depth of thetrough is determined by the expansibility required. The pressurenecessary to float a roof of usual weight is only a few inches of water.

Where a tank is large it is economical to use the arrangement shown inFigure 2. The trough is secured in the roof and the center part of theroof is equipped with a skirt extending into the trough as before. Byproviding a deeper trough and a longer skirtthe same degree ofexpansibility can be obtained as is obtained in the first arrangement,the moving parts being smaller. 1

It is necessary to prevent the roof from rotating. I accomplish this bproviding two or more closed tubes 9 noneakably secured to the tankroof, into each of which a pipe column 10 extends. braced within thetank and prevent the roof from rotating, yet allow it to movevertically.

When the roof is at its lowest position it rests on the columns 11 whichare braced within the tank.

It is to be noted that the pressures in the tank are very nearlyconstant. A pressure relief valve operated by change'in pressure wouldnot function here, but by providing a valve as in Figure 4 which dependson the position of the roof to operate it this difficulty is eliminated.This valve consists of a cup 12 secured to the tank roof, open end downand extending into a second cup 13 secured to vapor recovery system orsimp y to the outside of the tank. In this manner the roof ispreventedfrom over-traveling and the vapor is got permitted to blowthrough the roof sea The means above described for sealing the vaporoutlet is desirable for several reasons; it is reliable, free fromworking parts and is absolutely gas tight. However, there are conditionsin which such a valve would not be entirely satisfactory. Where anyliquid in the vapor lines except the condensate of the vapor itself isundesirable such a liquid sealed valve would not do. For suchinstallations I contem late the use of other valves. Any valve whic canbe operated by the movement of the roof is suitable, such valves as theordinary stockcock and others answer this requirement.

My present invention canbe very economically applied to old tanks. Bcutting the old roof free from the tank shell and providing the trough 1and the skirt 7 the old roof can be used as an expansion roof. Other omyis efiectedby using the old roof.

These columns are.-

By weighing my expansion roof with suitable ballast, pressures greaterthan atmos cured thereto, said tube extending upward pheric can bemaintained on the vapor in the tank. In storing liquids with high vaporpressure this would materially reduce the volume of vapor formed.

The principle of my liquid seal expansion roof can be utilized on allmanner of storage tanks and reservoirs for storage of other liquids thanoil, and I do not limit myself to the specific embodiments hereindescribed except as defined in the following claims. v

I claim as my invention:

'1. In vapor disposal means for an oil storage tank equipped with avapor sustained roof, a relief valve comprising: a first cupstationarily secured within said tank, open end up, said end beinghigher than the surface of said oil; a second cup secured to the roof ofsaid tank, open end down, and adapt ed to enter said first cup; and atube passing through the bottom of said first cup and sewithin said cupsto substantially the level of thetop of said firstcup the. opposite endofsaid tube communicating'with said-va or disposal means; said first cupbeing fille with a, I

liquid into which said second cup dips to 'form a gas tight seal betweensaid tube and cups; the larger of said cups stationarily secured withinsaid tank, open end up, said end being above the surface of said oil and-filled with a liquid; the smaller of said cups secured tosaid roof,open end down and.

adaptedto enter said lower cup;and means :Eor'conveying tank vapors fromwithin said smaller cup when said roof has lifted said smaller cupfromthe liquid in said lower cup. 1

In witness thatI claim the foregoin I have hereunto subscribed my namethis 2 th day of January, 1928. v

CHARLES BOHNHARDT.

